We will derive quantitative acoustic data that describes the development of speech production in infants and young children, as well as speech directed to them by adults, and to use this data to test and refine theories that explicate both the development and the internal structure of phonetic and phonologic ability in Homo sapiens. We have systematically recorded children from birth through the preschool years in their homes in natural situations at two week intervals. We will use the computer system that we have developed, supplemented by sound spectrograms, to derive formant frequencies and durations of vowels: onset spectra, burst and formant frequency patterns of consonants; and the fundamental frequency, amplitude, and durational correlates of suprasegmental intonation. The computer system also allows us to assess by psychoacoustic experiments, the linguistic salience of specific acoustic parameters. The theoretical issues that are of concern are: a) What innate biological mechanisms might be present in children that would be expressed as they acquire speech? b) What is the role of the child's adult caretakers in the acquisition of speech. Do adults provide "hypercorrect" acoustic cues to facilitate the child's acquisition of phonemic contrasts? c) What can we say concerning the linguistic salience and hierarchy of particular acoustic features from the appearance in the speech of young children and in the "hypercorrect" speech that may be directed to children by adults? d) What is the normal development of speech in children? Is the babbling stage disjoint from the early stages of work acquisition? Will children raised in different linguistic environments produce similar sounds in the babbling stage, or will their sounds reflect the phonetic inventory of the particular language that they're exposed to. Can we develop acoustic measures that will aid in the early detection and correction of pathologies?